Restoring spawning areas for salmon and trout not accessible for more than 100 years.
The Hiitolanjoki River, spanning 53 km and flowing from Finland to Russia, reaches Lake Ladoga, hosting the endangered Ladoga salmon population. Hydropower dams have threatened this unique salmon species and other vital fish, like brown trout and spined loach. Hiitolanjoki is crucial for Ladoga salmon spawning, yet dams impede migratory routes. After two decades of negotiations, the South Karelia Recreation Area Foundation acquired the dams, initiating a project to dismantle three dams (Kangaskoski, Lahnasenkoski, and Ritakoski) with support from various financiers. Dams at Kangaskoski and Lahnasenkoski were dismantled during 2021-2023, Ritakoski Dam was the last one to be dismantled in September 2023. The restoration benefits locals, conservationists, researchers, and tourists.
| Project status | Completed |
|---|---|
| Project type | Dam removal: demolition |
| Country | Finland |
| River | Hiitolanjoki |
| Removal date | September 2023 |
| Km opened | 6 km |
| Focal species | Land locked salmon (Salmo salar m. Sebago Girard) and brown trout (Salmo trutta) |
| Organisation | South Karelian Foundation for Recreation Areas |
| Website | Hiitolanjoki |
The dams are removed to return the original whitewater rapids, the main reproduction areas for salmonid and other riverine fish species, plus other biodiversity. Wild, unharnessed rapids, as well as migratory fish, are endangered as habitats and as species. Thus, the dam removals in Finland typically include building back the lost rapids. Without that part of the work, simply by removing the dam, the river’s slope underneath the removed dam would be easily too steep for the fish to swim up.
Furthermore, the crucial river habitat created by removing the dam would not support fish reproduction, could be dangerous to people, very hard to utilise for recreation and would also be a significant flaw in the landscape. By taking care of the landscaping and designing the environment for recreational use in the dismantling phase of the dams, the maintenance of the rapids and spawning areas will also be facilitated.
Positive changes in the river’s ecosystems were noticed right after the first dam was dismantled in the fall of 2021 at Kangaskoski. Salmonid’s spawning nests were observed in the restored rapids soon after the demolition. Several researchers now regularly monitor and study the river’s ecosystem and biota.
This project opened new spawning areas for salmon and trout not accessible for more than 100 years. Dam removal is a freshwater restoration measure to restore migratory routes, but efforts were also made to restore the habitats of the rapids left under the dams. The primary outcome was to ensure the wild reproduction of endangered salmonids in new accessible natural habitats.
The area located upstream of Ritakoski has plenty of ecologically important habitats in already free-running rapids in the main channel itself and in tributaries. The estimated production potential concerning the spawn of migratory salmon and trout in the Finnish sections is 5,000 – 11,000 migratory young fish per year. That would mean at least a doubling of the current production of the river.
In addition, dismantling the dam is vital for many other species besides fish. The nature of the riverbank reveals its diversity in different seasons. Among the mammals, the beaver, otter and fox live in the Hiitolanjoki area. Hiitolanjoki is also an important early spring base for migratory birds. There is also an abundance of different pollinators and other insects.
By completing this project, three opened rapids in river Hiitolanjoki will form an exceptionally stunning passage with a combined descent of 18 meters and form a passage for migrating fish to their traditional spawning places.
The Ritakoski River Restoration project, carried out by contractor Destia, has achieved significant milestones from its commencement on 1st August 2023 to its completion on 15th December 2023.
Initial Operations: The operation of the Ritakoski power plant ceased as planned at the end of July 2023. The construction site was prepared by removing surrounding trees, and construction of the submerged weir began by placing gravel and moraine materials.
Flow Direction Adjustments: After turbine operations stopped, river water was redirected through the opened dam, maintaining water levels above the dam. The turbine chamber was dried, turbines removed, and water flow resumed through the power plant.
Dam Removal: The dam’s concrete structures were removed with a machine rammer, and new pillars were cast from concrete due to the old pillars’ fragility.
Riverbed and Rapids Shaping: Riverbed and rapids were shaped to support fish migration, with loose boulders rearranged and sedimented materials from previous constructions tested for mercury content and safely relocated. New spawning areas were created using gravel and cobblestones as shelters for fish fry.
Landscaping and Recreational Development: Landscaping around the power plant area and rapids included creating safe walking trails and viewing points, enhancing the area’s recreational and tourist appeal.
Outcomes:
In the electrofishing survey conducted in Hiitolajoki, it was monitored up to 400 salmonids per 100 m2 – twice as much as 2023’s measurements! The result proves that the river habitat and the fish population will develop in the restored environment in a couple of years! (September 2024)
Funded by
